Method of providing an annular seal, and wellbore system

ABSTRACT

A method of providing an annular seal around a tubular in a wellbore penetrating a subsurface formation, the method comprising providing a tubular in the wellbore, wherein an annular space ( 18 ) is formed around the tubular; providing an annular gravel pack in the annular space; wherein the method further comprises arranging a band ( 9   a   , 9   b   , 9   c   , 9   d ) of gel-forming material around the tubular before providing the annular gravel pack, wherein the gel-forming material is swellable in a selected fluid, and wherein the annular seal is formed by contacting the band of gel-forming material with the selected fluid; and a wellbore system comprising a gravel-packed tubular in a wellbore, wherein the tubular is provided with a band of gel-forming material in a layer around the tubular, the band being surrounded by gravel ( 15 ), and wherein the gel-forming material is swellable in a selected fluid.

The present invention relates to a method of providing an annular sealand to a wellbore system.

In the production of fluids from a subsurface formation such as areservoir of hydrocarbon fluid via a wellbore formed in the earthformation it can be desired to prevent transfer of a selected fluidbetween the subsurface formation and the surface facility. For example,a hydrocarbon fluid reservoir often overlays a water-containing layer ofthe earth formation. After continued production of hydrocarbon oiland/or gas from the reservoir, the water level below the reservoir mayrise to the level of an intake zone of the wellbore. Also, under certainconditions of hydrocarbon fluid production an effect named“water-coning” may occur whereby water is drawn from thewater-containing layer to the wellbore intake zone. As a result anincreased amount of water will be produced, at the cost of production ofhydrocarbon fluid. Such undesired fluid production can significantlyreduce the economics of a hydrocarbon fluid prospect.

Hydrocarbon production wells are often extending horizontally can haveintake zones extending over hundreds of meters or even kilometres.Ingression of an unwanted fluid such as water in a relatively small partof the intake zone, e.g. though coning, can occur sometime after thestart of the production. It would then be desirable to isolate thesection of the intake zone, and perform a remedial action or close offthat zone.

Another situation in which zonal isolation in a gravel-packed completioncan be desired is a damaged gravel pack, leading to increased sandproduction.

In principle zonal isolation can be arranged by using expandablepackers. However, packers cannot be effectively used in case of agravel-packed well-completion. Gravel packing is often used for thecontrol and reduction of sand influx from the formation into theproduction conduit. Gravel packing as used herein refers to placinggravel and/or other particulate matter around production conduit as partof a well completion. For instance, in an open-hole completion, a gravelpack is typically positioned between the wall of the wellbore and aperforated base pipe. The gravel pack serves as a filter withholdingsand, additionally the base pipe can have sand-filtering means such as asand screen or perforations in the form of slots of suitable width towithhold sand. Alternatively, in a cased-hole completion, a gravel packis positioned between a casing string having perforations and aperforated base pipe, with or without additional sand-filtering means.

A gravel pack however stands in the way of expanding, eithermechanically or by swelling, of a conventional packer. At best, acompaction of gravel can be achieved, which may lead to a limited flowbarrier increase or sealing effect. SPE paper No. 122765 by R. Jansen etal. reports on using a conventional swellable packer in the context of agravel pack completion, but it is not disclosed that the packer providesa seal through the gravel pack.

International patent application publication No WO 2007/092082 disclosesa wellbore method and apparatus for completion, production andinjection, wherein a plurality of production intervals in the wellboreare segmented by packers. In the production tubing sections between thepackers sand screens are arranged. The packers can include swellableelements. After the packers were expanded to provide an annular seal andisolation between production tubing sections, gravel packing isinstalled around the sand screens.

Swell packers comprising shunt tubes, such as disclosed inEP-2184436-A2, still enable fluid flow through the shunt tube. Packersincluding shunt tubes thus only create a restriction in flow and areunable to provide full zonal isolation of the annular space.

There is a need for a simpler and more cost effective method that can beapplied for zonal isolation in gravel pack completions, in particularfor providing an annular seal in such a wellbore.

To this end, the present invention provides a method of providing anannular seal around a tubular in a wellbore penetrating a subsurfaceformation, the wellbore having a wellbore wall and the methodcomprising:

-   -   providing a tubular in the wellbore, wherein an annular space is        formed between the tubular and the wellbore wall;    -   providing an annular gravel pack in the annular space;

wherein the method further comprises:

-   -   arranging a band of solid gel-forming material around the        tubular before providing the annular gravel pack;    -   contacting the band of solid gel-forming material with a        selected fluid, wherein the solid gel-forming material becomes a        swellable gel;    -   swelling of the gel into the gravel to form the annular seal        between the tubular and the wellbore wall.

The invention is based on the insight gained by applicant that agel-forming material can swell to form a seal even when a gravel pack ispresent in the annulus, different from e.g. an inflatable packer or aswellable elastomer packer. A band of gel-forming material that isarranged as a layer around the tubular can thus swell to the oppositewall of the annular space, and will incorporate gravel particles in theswollen gel, which in fact reinforces the seal provided in this way.

Additionally this method creates true zonal isolation since there willbe no leak path through the gravel after the mobile gel has penetratedthe gravel.

In one embodiment the selected fluid contacting the at least one band ofgel-forming material is or forms part of a formation fluid entering thewellbore from the subsurface formation.

In one embodiment the contacting takes place at the time of abreakthrough of an unwanted formation fluid into the wellbore. In animportant application, the selected fluid is water or brine, so that theannual seal formed by activating the gel-forming process when and wherewater-coning occurs.

In one embodiment the band of gel-forming material forms a first band ofa plurality of bands of gel-forming material which are arranged aroundthe tubular in a longitudinally spaced manner, the plurality alsoincluding a second band of gel-forming material. Then, two annular sealsare formed by contacting the first and the second band with the selectedfluid, so as to provide a zonal isolated annular space, which is definedby the longitudinal spacing between the first and second band. Twoannular seals isolate the zone between them. If more than two bands arearranged along the tubular, different zones can be isolated by pairs ofannular seals. When the selected fluid activating the swelling is in theformation fluid, the position of influx determines automatically wherethe seals are formed.

In one embodiment, the method further comprises detecting which of theplurality of bands of gel-forming material has or have formed an annularseal. This can be of interest when the swelling and sealing takes placeautomatically by the influx of the selected fluid, where it can bedesired to perform a specific action in the thus isolated zone.

In one embodiment the method further comprises performing a remedialaction in the zonal isolated annular space.

The remedial action can e.g. be total shut off of a specific zone toprevent inflow of unwanted fluids. This can be achieved by thedeployment of a cementious material, resin or gel from within thetubular via openings in the tubular into the annular space, ans possiblyalso the surrounding formation. The tool used for this operation van berun using drillpipe, coiled tubing or wireline. For example, coiledtubing equipped with packer elements is run into the tubular andpositioned at the zone of interest. Packers are set within the tubularabove and below the zone of interest, corresponding to the annular zonethat isolated by the method of the invention. The isolated zone can nowbe shut off by injecting a cementious material, resin or gel.

Another remedial action can be a selective chemical treatment of thatzone or though that zone, e.g. with scale inhibiter, acid stimulation,or wax removal etc., to improve the inflow of hydrocarbons from thatzone.

A further remedial action can be the repair of a completion element,e.g. a damaged gravel pack in the annular isolated zone, e.g. bychemical sand consolidation. Thereby sand or gravel production from thatzone can be stopped.

In one embodiment the tubular is provided with one or more bands ofgel-forming material on surface, before installing the tubular in thewellbore. This makes installation of the bands simple, and provides forexample an easy and economic way of automatically sealing water-ingresszones during the production life of the wellbore.

In one embodiment the tubular has a wall and comprises at least one opensection with fluid inlet openings in the wall, and at least one closedsection with impermeable wall towards the annular space. Then the bandof gel-forming material is suitably arranged in the at least one closedsection.

In one embodiment the gel-forming material comprises a gel-formingcomponent selected from the group consisting of a layered silicate, aninorganic polymer, a superabsorbent polymer.

The invention moreover provides a wellbore system comprising agravel-packed tubular in a wellbore, wherein the tubular is providedwith a band of solid gel-forming material in a layer around the tubular,the band being surrounded by gravel, and wherein the gel-formingmaterial is adapted to become a swellable gel when contacted with aselected fluid.

The invention will now be further described by way of example and withreference to the drawings, wherein

FIG. 1 schematically shows a downhole section of a wellbore into which atubular with bands of gel-forming material is run;

FIG. 2 schematically shows the downhole section of the wellbore of FIG.1, while gravel is pumped into the annulus around the tubular;

FIG. 3 schematically shows the downhole section of the wellbore of FIGS.1 and 2 after an annular seals in accordance with the invention wereformed to provide a zonal isolation; and

FIG. 4 schematically shows an embodiment of a band of gel-formingmaterial.

Like reference numerals are used in the Figures to refer to the same orsimilar objects.

Reference is made to FIG. 1, showing a horizontal downhole section of awellbore 1 extending, normally from surface, into the earth andpenetrating a subsurface earth formation 3.

A tubular is provided in the wellbore by running production tubular 5 isinto the wellbore 1, indicated by the arrow. The production tubularcomprises open sections 8 a, 8 b, 8 c with inlet openings for fluidcommunication with the annulus, alternating with closed sections 9 a, 9b, 9 c. A plurality of bands 12 a, 12 b, 12 c of gel-forming materialare disposed exteriorly around the tubular 5, in the closed sections 9a,9 b,9 c. Arranging the bands was done in this example on surface,before running the tubular into the wellbore.

The length of an open section can e.g. be in the range of 1-500 m, suchas 10-200 m. The length of a closed section can be in the range of0.5-50 m, typically 1-5 meters. An open section can e.g. be providedwith perforations, slots, and/or a sand screen. The wellbore 1 is shownas an open-hole wellbore, but it will be understood that it can also becased and suitably provided with casing perforations to allow ingress offormation fluids to be produced to via the production tubing to surface.

FIG. 2 shows the production tubular when it is fully run into thewellbore 1, and while gravel 15 is being pumped via the downstream endof the production tubular 5 into the annular space 18, as indicated bythe arrows. Thus an annular gravel pack is provided in the annular space18. The bands of gel-forming material 9 a,9 b,9 c,9 d are surrounded bygravel 15. FIG. 2 depicts a wellbore system according to the invention.

FIG. 3 shows the wellbore system after some time of operation. Formationfluid is entering into the wellbore as indicated by the arrows.Formation fluid such as oil is in principle produced from formation 3,flowing through the gravel pack into the production tubing 5 viaopenings in the open sections, and from there to surface (not shown).During the lifetime of the well the constitution of formation fluid canvary along the length of the wellbore 1, i.e. can be different in thevarious virtual sections 20 a,20 b,20 c,20 d generally corresponding tothe open sections 8 a,8 b,8 c,8 d. In one type of applications it isdesired to produce predominantly hydrocarbons, such as oil. Suitablythen, the gel-forming material does not form a gel when coming incontact with the reservoir fluid that is desired to be produced, e.g.oil.

FIG. 3 shows the situation that the formation fluid flowing into thewell in the section 20 c is or contains a breakthrough fluid, e.g.water, such as at least 10 wt % water, or at least 50 wt % of water. Thegel-forming material of bands 12 a,12 b,12 c,12 d is a material thatforms gel when coming in contact with the breakthrough fluid. Thebreakthrough fluid is a selected fluid that can be regarded as anactivating fluid for the gel-forming material. The gel-forming materialof bands 12 b and 12 c comes in contact with the inflowing water, andthe bands swell through the gravel, until they meet the inner wall ofthe wellbore 1 (which can be uncased as shown, or cased), so as toprovide an annular seals 22 b, 22 c. The annular seals 22 b, 22 c form azonal isolation of section 20 c. The zonal isolation prevents flow offluid via the annulus in and out of the isolated zone, section 20 c inthis example. The bands 12 b and 12 c can be regarded as first andsecond bands of the plurality of bands of gel-forming material.

It is then for example possible to close the perforations/inlets in theopen section 12 c from inside the tubular 5, so that the water is notproduced to surface. It is now also possible to isolate an annular zonebetween two annular seals by straddling with packers that zone frominside the production tubing. Selective treatment of that zone to eitherstimulate or shut off production is now possible. It is also possible tomonitor and measure the production from that specific zone.

If the wellbore 1 is non-horizontal such as a substantially verticalwell, over the lifetime of the well the level of the oil/water contactmay rise due to depletion of the oil reservoir, and thus give rise toingress of water from the lowest sections, which can be shut off in thisway.

Forming one annular seal can for example be sufficient if the mostdownhole part of the wellbore annulus is to be sealed off.

The gel-forming material can be gel-forming when the selected fluid iswater. Alternatively, it can be gel-forming when contacting with oil,e.g. crude. It is also possible that the gel-forming material isgel-forming when being contacted with either one or both of water andoil. Herein water is meant to include brine.

Suitable gel-forming material, when the selected fluid is or compriseswater, is or comprises an inorganic polymer, in particular a layeredsilicate. Suitable layered silicates are sold by Rockwood AdditivesLimited under the trademark Laponite. Suitable gel-forming Laponitegrades are e.g. grades RD, XLG, D, DF, XL21, HW, or LV. Relevant CASNos. of suitable Laponite materials are 53320-86-8 and 64060-48-6.Relevant EINECS Nos. of suitable Laponite materials are 258-476-2 and285-349-9. A band of gel-forming material containing Laponite can forexample be made by putting Laponite powder in a mould and applyingpressure until a solid Laponite band is formed. Other components such ase.g. a filler or additives can be added in the moulding process. Thegel-forming band can be placed with this method straight on the basepipe as well. Alternatively two halve moon bands can be preparedseparately and subsequently they can be glued in place with epoxy resin.The Laponite containing band can also be provided on a carrier orsupport.

Another suitable gel-forming material, when the selected fluid is orcomprises water, is or comprises a superabsorbent, such as apolyacrylate and/or polyacrylamide based superabsobent. The polyacrylateand/or polyacrylamide can be cross-linked. Suitable superabsorbents aresold by BASF under the trademark Luquasorb. Another suitablesuperabsorbent is sold by Imbibitive Technologies America Inc. (IMBTECHAMERICA) under the trademark AquaBiber.

Bands of gel-forming material can be made from superabsorbants, e.g.Luquasorb or AquaBiber materials, by putting grinded superabsorbent in amould and applying pressure thereby creating a solid band. Depending onthe salinity of the surrounding formation or completion fluids between1-50 w/w % of metal halides, based on the mass of superabsorbent, can beadded. The metal halides are preferably NaCl or KCl. Other componentssuch as e.g. a filler or additives can be added as well. The gel-formingband can be placed with this method straight on the base pipe as well.In another embodiment, two half moon shaped bands can be preparedseparately and subsequently they can be glued in place with epoxy resin.

Suitable gel-forming material, when the selected fluid is or comprisesoil, is e.g. an alkylstyrene copolymer, e.g. the material sold under thetrademark Imbiber by Imbibitive Technologies America Inc. (IMBTECHAMERICA). The same band forming process as for superabsorbents Luquasorbcan for example be used.

The gel-forming material is suitably not free-flowing, before it iscontacted with the selected fluid. For example, the gel-forming materialcan be solid, highly viscous, or thixotropic. Thixotropic materials donot freely flow, but flow when pressure is applied, i.e. show abehaviour like toothpaste. The gel-forming material does not contain asubstantial quantity of a solvent, e.g. less than 20 wt %, or less than5 wt %, in particular no solvent.

It can be desired to apply a gel-forming material that is forming a gelwhen being contacted with either one or both of hydrocarbons, e.g. oil,and water. That can for example be achieved by a mixture of Imbibermaterial with either Luquasorb or Aquabiber material, such as a mixtureof a weight ratio between 20/80 and 80/20 can be used to have agel-forming band that swells when being contacted with water and/orhydrocarbons.

The gel-forming material is suitably stable at downhole conditionsbetween 50-150° C. for at least one week, preferably at least one month,more preferably at least one year. Stability means that the materialremains intact, in its unswollen and/or swollen state, at downholetemperatures, in particular between 50-150° C. and under contact withdown hole fluids, like crude, brine, and gases.

The width of the band can be suitably chosen, and will typically be inthe range of 0.1-100 m, preferably 0.25-25 m.

The gel-forming material swells when being contacted with the selectedfluid. Suitably, the maximum swelling ratio, measured as the maximumthickness of the band achieved after long swelling in an open space,divided by the unswollen thickness, is in the range of 1.1-50,preferably 2-10, for example 5. The thickness of the band is suitablyadapted to the size of the annulus and the maximum swelling ratio. Thethickness will typically be in the range of 0.5 mm to 30 mm, preferably1-20 mm. Suitably the thickness is chosen such that a swelling between10 and 90% of the maximum swelling ratio is needed to achieve an annularseal, not taking the gravel into account. For example, with a tubular of12.7 cm in an open hole of 20.3 cm, the annulus is 3.8 cm thick.

Then, for example, a band with a maximum swelling ratio of 5 and athickness of 1.5 cm will provide a seal at a swelling ratio of 2.5 inthickness (not taking gravel into account), i.e. 50% of the maximumswelling ratio.

Swelling ratio is suitably chosen such that the annular seal is able towithstand a differential pressure of 1-50 bars per meter of band formed.

The bands of gel-forming material can in principle be arranged anywherealong the tubular. For bands shorter than a pipe element of theproduction tubular, the position along the pipe element can sometimes beselected. FIG. 4 shows a particular example of a relatively shortgel-forming band arranged around a production tubular 30. The productiontubular 5 is formed of a plurality of pipe elements, of which two pipeelements 31,32 are shown that are connected by a pin- and box connection35. The pin-and-box connection forms 35 forms a shoulder 37. The band ofgel-forming material 40 is arranged in the vicinity of the shoulder 37,around the tubular 31 providing the pin-part if the connection. The bandis shown here flush with the diameter of the box part. It will beunderstood that the band can be thinner, or somewhat thicker as neededfor the seal. An advantage of this arrangement is that the band 40 isprotected, at least partially, by the shoulder when running the tubularin the wellbore, and that no or only a minimum obstacle is formed by theband for running the tubular in. As additional protection, a protectionlayer or skirt of a perforated material, like e.g. a metal gaze 42 canbe provided at the external surface facing the annulus, and possibly atthe sides. Such a protection skirt would not hamper the swelling of thegel. The band can have a support layer at the tubular side 44, which canbe suitably fastened to the tubular, e.g. glued.

Running the bands of gel-forming material wrapped around the tubular aspart of the completion installation is simple and cost-effective, andthe position of the potential annular seals can be determined with highaccuracy. Activating the swelling can occur quasi automatically “insitu” by the ingress of a formation fluid containing the selectedactivating fluid, e.g. water, thus no further equipment is required inthis case. As an alternative it is also possible to start thegel-forming process by deliberately feeding the selected fluid to intothe annulus, so as to cause the annular seal to be formed. This can forexample be achieved from within the tubular via the openings in the opensections. It is also possible to arrange separate conduits and/orreservoirs for the selected fluid, which can be operated remotelycontrolled from surface so as to contact the bands of gel-formingmaterial and cause their swelling, e.g. triggered by a pressure pulse, adart or ball from surface.

The gel-forming material swells when it is contacted with a selectedfluid that is attracted into the matrix of the material, and thusactivates the swelling. Swelling in suitable materials as layeredsilicates, superabsorbents or Imbiber discussed hereinabove, is causedby physico-chemical processes that are reversible, so that bonds onmolecular level, such as hydrogen bridges, are reversibly formed. Theswelling or swollen gel still has some ability to flow/rearrange, andcan sometimes be regarded as a highly viscous fluid. Someflowing/rearranging properties are needed to penetrate through a gravelpack, wherein on a microscopic level the material distributes throughthe pore space created by the gravel particles. The swelling or swollengel can be a thixotropic material. For comparison, a swellableelastomer, such as being used for swellable packers, are chemicallycross-linked structures, e.g. made from acrylonitrile butadiene rubber(NBR) or ethylene propylene dimonomer (EPDM). See e.g. the Handbook ofPlastics, Elastomers & Composites, Harper, Charles A. (Ed.), 4thEdition, McGraw-Hill, 2002. Chemically crosslinked materials cannot flowand cannot penetrate through the pore space created by the gravel pack.

A gel according to the invention may be defined as a material which isable to flow only after overcoming an initial yield stress. In apractical embodiment, the yield stress may exceed about 100 Pa, forinstance more than 200 Pa. An upper limit of the yield stress may beabout 5 kPa. The solid gel-forming material is for instance able toabsorb water to transform into the swellable gel.

EXAMPLE

A lab scale arrangement of tubular was built, with a 12.5 cm (o.d.)inner tube coaxially arranged in a 17.8 cm (i.d.) outer tube. The innertube was provided with a 10 cm wide band of a gel-forming material madeof Luquasorb 1010. The thickness of the gel-forming band was initially 5millimetres. Water was pumped through the annulus. Pressure started toincrease over time, after about 72 hours, indicating that thegel-forming system was swelling and penetrating through the gravel sand,so as to form an annular seal. The experiment was stopped when the sealwas able to withstand a pressure of 1 MPa differential pressure over theseal.

The present invention is not limited to the above described embodimentsthereof, wherein various amendments are conceivable within the scope ofthe appended claims. Features of respective embodiments may for instancebe combined.

1. A method of providing an annular seal around a tubular in a wellborepenetrating a subsurface formation, the wellbore having a wellbore walland the method comprising: providing a tubular in the wellbore, whereinan annular space is formed between the tubular and the wellbore wall;providing an annular gravel pack in the annular space; wherein themethod further comprises: arranging a band of solid gel-forming materialaround the tubular before providing the annular gravel pack; contactingthe band of solid gel-forming material with a selected fluid, whereinthe solid gel-forming material becomes a swellable gel; swelling of thegel into the gravel to form the annular seal between the tubular and thewellbore wall.
 2. The method according to claim 1, wherein the selectedfluid contacting the at least one band of gel-forming material is orforms part of a formation fluid entering the wellbore from thesubsurface formation.
 3. The method according to claim 1, wherein thecontacting takes place at the time of a breakthrough of an unwantedformation fluid into the wellbore.
 4. The method according to claim 1,wherein the band of gel-forming material forms a first band of aplurality of bands of gel-forming material which are arranged around thetubular in a longitudinally spaced manner, the plurality also includinga second band of gel-forming material, and wherein two annular seals areformed by contacting the first and the second band with the selectedfluid, so as to provide a zonal isolated annular space.
 5. The methodaccording claim 4, wherein the method further comprises detecting whichof the plurality of bands of gel-forming material has or have formed anannular seal.
 6. The method according to claim 4, wherein the methodfurther comprises performing a remedial action in the zonal isolatedannular space.
 7. The method according to claim 1, wherein the remedialaction comprises at least one operation selected from the groupconsisting of shutting of fluid flow in or into that zone, chemicaltreatment, a repair operation of a well completion element.
 8. Themethod according to claim 1, wherein the tubular is provided with one ormore bands of gel-forming material on surface, before installing thetubular in the wellbore.
 9. The method according to claim 1, wherein thetubular has a wall and comprises at least one open section with fluidinlet openings in the wall, and at least one closed section withimpermeable wall towards the annular space, and wherein the band ofgel-forming material is arranged in the at least one closed section. 10.The method according to claim 9, wherein the swollen gel forming theannular seal includes gravel.
 11. The method according to claim 1,wherein the gel-forming material comprises a gel-forming componentselected from the group consisting of a layered silicate, an inorganicpolymer, a superabsorbent.
 12. The method according to claim 1, whereinthe selected fluid causing the gel-forming material to swell when beingcontacted with the gel-forming material comprises water, hydrocarbonoil, or water and hydrocarbon oil.
 13. A wellbore system comprising agravel-packed tubular in a wellbore, wherein the tubular is providedwith a band of solid gel-forming material in a layer around the tubular,the band being surrounded by gravel, and wherein the solid gel-formingmaterial is adapted to become a swellable gel when contacted with aselected fluid.
 14. The wellbore system according to claim 13, whereinthe band of gel-forming material forms a first band of a plurality ofbands of gel-forming materials which are arranged around the tubular ina longitudinally spaced manner, the plurality also including a secondband of gel-forming material.
 15. The wellbore system according to claim13, wherein the tubular has a wall and comprises at least one opensection with fluid inlet openings in the wall, and at least one closedsection with impermeable wall towards the annular space, and wherein theband of gel-forming material is arranged in the at least one chosen.